1. Field of the Invention
The present invention relates to a cryogenic refrigerator and, more particularly, to a cryogenic refrigerator using a cycle such as Gifford-McMahon cycle.
2. Description of the Related Art
A typical conventional cryogenic refrigerator of the type described above is arranged such that a refrigerant such as helium or the like is circulated between a compressor and a working chamber defined between a piston and a cylinder in response to the opening and closing operation of a valve activated in synchronism with the movement of the piston, and when the refrigerant is adiabatically expanded in the working chamber, a cryogenic temperature is generated in the cylinder.
This type of conventional cryogenic refrigerator suffers, however, from the following disadvantages.
At the time of starting the refrigerator, the working chamber needs to be filled with the refrigerant, but, in this case, it suffices to deliver a relatively small amount of refrigerant from the compressor. However, since the delivery capacity of the compressor is constant, the refrigerant the pressure of which is excessively high at the time of starting the refrigerator must be fed back to the suction side of the compressor through a relief valve. For this reason, the capacity of the compressor cannot fully be used, and much time is required to bring the cryogenic refrigerator into a stable operation state after it has been started, which means that the machine involves disadvantageously low efficiency.